In view of protecting the environment, fuel vapor has been controlled besides the exhaust emission control. According to the regulation established by the Environmental Protection Agency (EPA) and the California Air Resourced Board (CARB), a leak detection of the fuel vapor from a fuel tank is required.
A conventional leak check system shown in JP-10-90107A, which is a counterpart of U.S. Pat. No. 5,890,474, has a pump which generate a pressure gradient between an inside and an outside of a fuel tank. When a leakage of fuel vapor from the fuel tank, a load of a motor driving the pump fluctuates. The detection of fuel vapor leakage is conducted by checking the fluctuation of the motor load.
The pump has sliding portions such as a piston and a cylinder or a vane and a housing in order to generate a pressure gradient. When the pump is operated, foreign particles due to an abrasion in the sliding portion may be produced. The foreign particles may be scattered to cause some electric problems, such as short circuit, in a control circuit for the motor. Furthermore, the foreign particles may cause the motor to be stuck.